After completing a second autonomous arrested landing on the nuclear-powered carrier, the 60-foot-wingspan X-47B was angling in for a third touch-down when it detected an anomaly in its own navigation computer and decided, all on its own, to abort the landing, pulling up just short of the flattop’s thousand-foot deck.

According to the Navy, the drone was about four miles behind the ship, with its arrestor hook and landing gear already down, when one of its routine health checks revealed an unspecified glitch in a computer subsystem.

The drone, developed since 2007 at a cost of around $2 billion, constantly performs countless checks on its own systems, a necessary precaution given its high degree of autonomy. The X-47B follows pre-programmed mission scripts, deviating only slightly to avoid obstacles and dangers it senses on its own. Human operators monitor the flight via radar and radio but rarely intervene.

Detecting the anomaly the jet-propelled, Northrop Grumman-built robot decided — without any human intervention — to wave off. The test drone flew past the carrier and reported its problem to human controllers on the carrier who then directed the ‘bot to an airfield ashore, where it apparently performed a flawless landing.

Two things are worth mentioning.

First, the Navy’s new killer drone detected a problem and made the proper decision before its human minders discovered it, thus boosting mission safety.